The survey of the wild animals, published in the journal Nature, builds on laboratory work which also suggests that male frogs can be feminised through exposure to the weedkiller.
They also argued over-use of the company's weedkiller Roundup, the chemical treatment the alfalfa is modified to be resistant to, could cause pollution of ground water and lead to resistant "super-weeds".
Such sterile fields will offer little or no food or shelter to wildlife, and there is already evidence that the genes for herbicide resistance can spread to wild relatives of crop plants, leaving us with weeds resistant to weedkiller.